?Silicon mullite brick is an aluminum-silicon-based material obtained by sintering silicon carbide, mullite, or bauxite clinker at high temperatures. The main crystalline phase of this material is corundum, mullite, and silicon carbide, and contains a small amount of cristobalite, because of its good wear resistance, high mechanical strength, excellent corrosion resistance, and thermal shock stability, it can be widely used in various parts of cement rotary kilns except the firing zone. For various multiphase materials composed of corundum, mullite, and silicon carbide as the main crystalline phases, predecessors have carried out relatively systematic research.
In recent years, with the upgrading of cement production equipment and the change of fuel used, the use environment of cement kiln lining materials has become more and more severe, and some high-temperature properties of ordinary silica mullite bricks, especially thermal shock stability, cannot meet the requirements for use. Therefore, we have carried out a series of researches on the performance optimization of silica mullite bricks. Yao Feng et al. used high alumina bauxite clinker as aggregate and added fused brown corundum, silicon carbide, and a-Al2O3 micro powder to the matrix. Through reasonable particle gradation, high-pressure molding and high-temperature sintering were used.
Silica Mullite Brick. The experiment shows that when the addition amount of a-Al2O3 is 6%, the performance of the obtained sample reaches the best state, its bulk density is 2.64g/cm3, the thermal shock stability exceeds 30 times (1100 ? water cooling), and the high temperature wear volume is 1.16cm3, the softening temperature under load is 1700? (0.6%), the compressive strength is 152MPa, and the thermal conductivity is 1.75W/(m?k). The product has been used by Shaanxi Yaobai Cement Group, Hebei Luquan Quzhai Cement, Dengfeng Hongchang Cement, and other enterprises in the upper and lower transition zones of 2500t/d and 5000t/d large-scale cement rotary kilns. The daily wear rate is only 0.1mm, and there is no peeling. , headshot phenomenon, life expectancy is more than one year. However, the disadvantage of this product is that the cost of raw materials is high, and the energy consumption is high during high-temperature firing.
Ding Jinxing et al. used high alumina bauxite clinker and SiC fine powder as the main raw materials, added andalusite with three particle sizes (3~1mm, 1~0mm, <0.074mm) respectively, and fired at 1480?×3h. The effects of andalusite addition and particle size on the properties of silica mullite bricks were investigated. The experiment shows that the andalusite added to the silica mullite brick is multisized at high temperature, which will form a staggered and compact mullite structure, which can resist the expansion of internal cracks in the product when the temperature changes rapidly, thereby improving the thermal shock stability of the material. The compact mullite formed after andalusite mullite is not only beneficial to the improvement of the thermal shock stability of the material but also can increase the softening temperature under the load of the silica mullite brick. The softening temperature of Mo bricks under load gradually increases. But also due to the high price of andalusite added in the silica mullite brick, the cost of raw materials increases.
Liu Zhenying et al. studied the effect of zircon sand (ZrO267.02%, SiO231.93%) addition on the properties of silicon mullite bricks using super high alumina bauxite and silicon carbide as the main raw materials. The results show that: when the addition of zircon sand gradually increases, the bulk density and compressive strength of the sample show a trend of increasing first and then decreasing. In addition, the thermal shock stability of the sample is significantly improved. When the sand addition amount is 10%~15%, the performance of the sample is better.
After an appropriate amount of zircon sand is added to the sample, the specific reaction formula during the sintering process is shown in formula 1. On the one hand, the content of mullite in the matrix will be increased to improve the high-temperature performance of the silica mullite brick, and on the other hand, the generated zirconia will be accompanied by The crystal transformation will absorb the energy of the main crack expansion, eliminate the thermal stress, and play the role of phase transformation and toughening, thereby improving the thermal shock stability of the product. However, if too much zircon sand is added, too much mullite will be formed, resulting in volume expansion, resulting in a decrease in strength.
2ZrSiO4+3Al2O3=3Al2O3·2SiO2+2ZrO2 (1)
Li Yuanjin et al. used mullite, bauxite homogeneous material, silicon carbide, and andalusite as the main raw materials, and developed a silicon mullite brick with good thermal shock resistance and low thermal conductivity, and used mullite, bauxite homogeneous material, silicon carbide, and andalusite as the main raw materials. The structure and shape were designed, and a low thermal conductivity multi-layer composite mullite brick was developed. Experiments show that: with 70% mullite as aggregate and 80% homogeneous material as a matrix, adding 12% silicon carbide and 10~12% andalusite powder, the prepared silica mullite working layer has a higher load softening temperature and good thermal shock resistance. When the working layer of the silica mullite brick and the thermal insulation layer are inlaid arc-shaped combined structures, and the shape of the opening of the thermal insulation layer is a trapezoidal dovetail groove structure with a hypotenuse angle of 45°, the prepared low thermal conductivity multilayer composite mullite brick has thermal conductivity. The rate is low, and the thermal matching between the brick layers is good. This product is used in the transition zone of the cement rotary kiln and has achieved good results. Compared with the traditional silica mulberry brick, the temperature of the cylinder can be reduced by 50~80?, which can save energy and reduce emissions in the cement industry, and realize the lightening of the kiln. to a positive impetus.
Wang Qiang et al. used high-alumina bauxite clinker and silicon carbide as the main raw materials to prepare silicon mullite bricks and studied the influence of silicon carbide particle size and addition amount on the properties of silicon mulberry bricks. The results show that when the addition amount of silicon carbide is 15%~20%, the properties of the silica mullite brick are better, and increasing the addition amount of fine particles is beneficial to the improvement of the compressive strength and the reduction of the apparent porosity of the sample. Increasing the particle size of the fine powder is beneficial to improve the thermal shock resistance of the silicon carbide. When the silicon carbide is compounded with two 10 kinds of a fine powder, the performance of the silicon mulberry brick is the best.
